Markers are commonly used to demarcate the edges of roadways, parking lots, airport runways and taxiways, sidewalks, stairways and trails. The markers enhance safety by providing a visual assessment of safe boundaries. Markers often incorporate passive reflectors to reflect incident light back to an observer. Observable reflectivity, which pinpoints the marker's position, depends upon a directional incident light beam for reflection. Retroreflective markers for roadway applications typically have an inclined front face at a suitable angle for reflecting incident light and sometimes allowing the front face of the marker to be wiped clean, for example, through contact with vehicle tires. Environmental conditions, such as rain or snow, can impair reflection of an incident light beam. Further, terrain may be such that a incident light beam from, for example, a car or bicycle headlights, does not directly strike the marker's passive reflector. In addition, retroreflective qualities tend to decrease over time due to ultraviolet degradation, moisture creep and cracking.
As an alternative to passive illumination, various markers having an independent light source have been described. Unlike retroreflective markers, lighted markers require some type of power source. The power source may be external, such as, for example, electrical wiring. Internal power sources have also been used. Solar powered markers having one or more photovoltaic cells generate electricity during the day and charge a capacitor or rechargeable battery for use at night. Photovoltaic cells tend to be easily damaged, and their electrical generation is heavily impacted by environmental conditions. For example, on cloudy days or during winter months, there is less daylight available for charging. Further, when photovoltaic cells are scratched or covered with dirt or snow, power generation is hindered.
Pavement markers having a light source powered internally by non-photovoltaic means have been described. For example, certain pavement markers utilizing the conversion of mechanical energy in the form of vibrational energy into electrical energy are known. The vibrational energy is generated when vehicles run on the roadway. As with photovoltaic cells, sufficient power generation is problematic in areas of fluctuating or low traffic in providing continuous overnight power.
In contrast to photovoltaic cells, which harvest incident light to generate electricity, thermoelectric cells generate electricity based on a thermal gradient existing about the thermoelectric cells. For example, a thermal gradient can exist between a pavement surface and the earth surrounding the pavement surface. Thermoelectric generation of electricity takes place with either variation of thermal gradient-electricity generation occurs when one side of the thermoelectric cell is either hotter or colder than its surrounding environment. Since thermoelectric cells do not require direct exposure to sunlight, they can be deployed within a protective housing to prevent damage.
In view of the foregoing, markers not relying solely on passive reflection or an inconsistent power source for illumination are likely to be of considerable benefit. For example, markers having a thermoelectric power generation unit for operating an internal light source would likely have a long useful lifetime and be operable under nearly any variety of surrounding environmental conditions.